A retractor for a vehicle seat belt contains a vehicle sensor, which responds to changes in the vehicle acceleration or deceleration occurring in a vehicle crash. The vehicle sensor is one of two sensor inertial mechanisms within the retractor; the other sensor means detects pay out of the webbing from the retractor due to the movement of a vehicle occupant when the vehicle decreases or increases in speed. The second mechanism is often called a webbing sensor.
The vehicle sensor comprises an inertial mass either in the form of a ball or a hollow shaped tube acting on a pin or a mass with a relatively high center of gravity located above a narrow base. Movement of the mass acts on a vehicle sensor lever positioned in close proximity to the mass to move a toothed portion of the vehicle sensor lever into engagement with teeth on a spool or a ratchet thus initiating the locking of the retractor spool and preventing further pay out of the webbing.
A typical retractor, including the vehicle sensor, is formed by many cooperating components. One of the problems associated with prior art retractors is that each component can vary in size due to environmental changes such as changes in temperature during the component manufacturing process. For example, components vary in dimensions due to multi cavity tools where more than one component is molded in sequence or at the same time. Also if large volumes of components are manufactured the molding tool may deteriorate or wear causing variation in component sizes. The variation in sizes creates variability in the relationship between each component. This is particularly undesirable in the vehicle sensor as the spacing between the spool teeth and the vehicle sensor locking teeth requires precision. The variation in the gap between the spool or ratchet teeth and the vehicle sensor locking tooth gives poor repeatability of the vehicle sensor's performance and controls the retractors locking. The space between the spool or ratchet teeth and the vehicle sensor locking tooth is called the "tip gap".
If the gap between the vehicle sensor lever and the spool teeth is too narrow the vehicle sensor lever may engage with the spool teeth and lock the retractor in a non-emergency situation. This can create discomfort for the occupant with the seat belt "jamming". In the case of an inertial mass in the shape of a ball, the ball rests on a socket and is free to move upon a change in position of the vehicle and retractor. The ball may cooperate directly or indirectly with a vehicle sensor lever. Alternatively the vehicle sensor may contain a cap or lid which sits directly over the inertial mass, which cooperates with the vehicle sensor lever. Upon displacement of the inertial mass the vehicle sensor lever is lifted either via the vehicle sensor inertia cap, directly by the mass or by a system of levers. The vehicle sensor lever is pushed upwards and engages with the teeth on the retractor spool thereby locking the retractor spool and preventing further rotation.
If the various retractor components have changed in size, thus creating a varying "tip gap", and if the vehicle is positioned at an angle the vehicle occupant may not be able to remove the webbing from the retractor rendering the seat belt unusable or creating a very sensitive belt which acknowledges and locks the retractor under non-emergency situations.
It is required that all retractors lock within specific pay out of webbing under certain vehicle acceleration and declaration conditions. With wide variations in component sizes the retractor locking times will vary and therefore different amounts of webbing will be released from the retractor. Such variations result in poor performance and efficiency of the seat belt. The higher the variation in the vehicle sensor performance, the higher the likelihood of experiencing high pay out of webbing which will not provide the most effective protection to the vehicle occupant.